This invention relates generally to piezoelectric transducers for generating an audible signal and more particularly relates to a manner of electrically connecting a printed circuit board within the casing of the transducer to the piezoelectric disk also within the casing to provide both a more durable electrical connection and also reduce the cost of assembling the transducers.
Piezoelectric transducers for use as audible signals have long been well known in the prior art. Their purpose is to generate a sound for use as an audible alarm or other audible signal. A piezoelectric transducer has a piezoelectric disk which is a metal disk with a piezoelectric crystal material bonded on the disk. The application of a voltage to the crystal causes the crystal to deform and thereby bend the metal disk. A periodic electrical signal is applied to the crystal to control its deformation and causes the disk to alternately bend in one axial direction and then in the opposite axial direction so that the piezoelectric disk alternately becomes convex and concave. This motion generates compressions and rarefactions in the adjacent air at audio frequencies and thereby generates a sound.
The principal components of a piezoelectric transducer are the piezoelectric disk and a circuit on a printed circuit (PC) board that is electrically connected to the disk for driving the disk in vibration at audio frequencies. Those components are usually housed in a cylindrical casing. There are at least two electrical connections from the PC board to the disk, one to the metal and one to the piezoelectric material. Typically, the metal disk is circular and the piezoelectric material is also circular but smaller in diameter so that the piezoelectric disk has an outer, annular area of bare metal to which one electrical connection is made to the PC board. Inwardly of that annular bare metal area is the circular piezoelectric crystal disk that is bonded to the metal disk. A second electrical connection is made from the PC board to the piezoelectric material. The circuit on the PC board generates the electrical signal that drives the piezoelectric disk in mechanical vibration to generate the sound.
Current manufacturing procedures for making the electrical connections from the PC board to the piezoelectric disk require soldering, usually by labor intensive manual hand soldering, of at least two wires. Each wire is soldered at one end to the PC board and at its other end to the piezoelectric disk. The need for hand soldering is a significant part of the cost of manufacturing and therefore increases the cost of the finished product. Consequently, there is a need for a manner of making these electrical connections in a way that can eliminate the need for hand soldering in order to reduce the cost of the piezoelectric transducer. Most desirably, there is a need to make these electrical connections in manner that can be automated, such as with the use of robots, to further reduce their costs of manufacture.
The need for soldering, whether or not by hand, also decreases the reliability, durability and life expectancy of the piezoelectric transducers that are manufactured in the prior art manner. The reason is that heat from the soldering process, which is applied to the piezoelectric disk and to the wires, stresses both. This heat stress can permanently distort the piezoelectric disk from its planar shape thereby causing a distortion of the sound it produces and making it fit improperly within its casing. Additionally, the heat stress of the fine wire conductors weakens them making them more susceptible to mechanical breakdown from metal fatigue as a result of the sonic vibrations to which the wires are subjected during use over a period of time. Consequently, there is also a need to not only eliminate hand soldering, but also to completely eliminate the use of the heat necessary for soldering in order to electrically connect the PC board to the piezoelectric disk. Elimination of soldering eliminates the heat stress and thereby improves the reliability, durability and lifetime of piezoelectric transducers.